Definition of loudspeaker: An electroacoustic transducer that converts an electrical signal into an acoustic signal and radiates it into the air. Speaker is our common name for speakers, here is an example of electric speakers.

 

Motorized speakers

 

The pronunciation principle of the speaker

Simply put, it is a energized coil, generating a magnetic field, and the magnetic circuit magnetic field work together to generate a downward or upward force, drive the paper cone to move, and the paper cone pushes the air to make a sound.

 

List of commonly used specifications

 

List of common speaker specifications

 

Electric speakers generally consist of 3 parts

(1) Magnetic circuit system: T iron, Wals, magnet, anti-magnetic cover;

(2) Vibration system: voice coil, paper cone, dust cap, bounce wave, brocade thread;

(3) Support system: basin frame, glue, magnetic fluid.

 

Introduction to magnetic circuit systems

 

1. Anti-magnetic cover

The role of the magnetic cover, together with the secondary magnetic, works together to play the role of anti-magnetism.

Main test items: inner diameter tolerance +0.5/-0mm, height tolerance ±0.3mm; Thickness tolerance +0.05/-0mm, appearance: rust, deformation, electroplating is poor, blistering, plating peeling, etc.

 

2. Magnets

Function: Provide magnetic energy, the magnets we use are artificial magnets, there are the following:

Aluminum, nickel, cobalt alloy (Alnico), high magnetic energy product, low coercive magnetic force, easier to demagnetize, generally made thicker, made into a cylindrical shape.

Rare earth permanent magnet material (NdFeB), high coercivity, high residual magnetism, high magnetic energy product, disadvantages: low working temperature, easy to rust, expensive.

Ferrite, is our commonly used external magnetic horn, its coercivity between Alnico and NdFeB, low residual magnetism, generally made into a flat shape, cheap, disadvantages: easy magnetic, relatively large volume.

 

Main detection items:

Structural dimensions: outer diameter tolerance ± 20%, inner diameter tolerance ± 20%, thickness tolerance ± 0.1mm;

Appearance inspection: crushing, crushing magnetism, iron powder, rust powder, etc.

Magnetic properties: post-assembly testing, sensitivity, etc.

 

ALFeB AlNiCo Ferrite comparison

 

ALFeB AlNiCo Ferrite comparison

 

3. Huaji

The role of T iron and Wass: is to direct one of the magnetic poles of the magnet to the other end of the magnetic gap, usually made of soft iron or low carbon steel, the appearance is multicolored, silver white, baked black and so on.

Huasi Testing Project:

Outer diameter tolerance (+0.5/0 with magnetic cover) Without magnetic cover: ±0.5mm

The tolerance of the middle hole is ±0.05mm

Thickness less than or equal to tolerance ± 0.2mm, greater than 4mm ± 0.3mm

Rivet diameter, height tolerance ± 0.10mm

The distance tolerance between the rivets ± 0.10mm

Appearance inspection: whether the middle hole is eccentric, not round, burr, unequal appearance.

 

4.T iron

Huasi Testing Project:

Bottom plate outer diameter tolerance± 0.5mm

Midcolumn tolerance -0.05

The height tolerance of the middle column ± 0.2mm

Solid magnetic bit tolerance ± 0.5mm

The bottom plate thickness ± 0.20mm

Appearance inspection: eccentricity, skew, burr, looseness of the middle column. Rust, poor plating, peeling of the plating, and differences in plating color.

 

Introduction to vibration systems

 

1. Voice coil

We generally describe as: ASV: 25.5*28*3.7*0.26 4F ASV: for voice coil tube material, SV voice coil line is SV line, 25.5: voice coil inner diameter, 28 is voice coil height, 3.7 DC impedance, 0.26 voice coil wire diameter, 4F layer number If not written, the DC resistance Re for the 2F voice coil should generally be preset, or determined according to the rated impedance Znom:

Znom =(1.05~1.10)* Re

 

Kraft Paper PSV/PL

Cable paper (kraft paper) with a maximum continuous operating temperature of 180 oC is used, which is characterized by light weight, good insulation and low price. Its thickness is: 0.03 0.05 0.07 0.10 0.13 0.17

Aluminium Duralumin AL/ASV

Aluminum foil with case hardened and cleaned alloy has a maximum continuous working temperature of 200 oC, which has the characteristics of high temperature resistance and high strength. Aluminum foil has two kinds of black and white, black aluminum foil has the advantages of good insulation performance and fast heat transfer. Its thickness is: 0.05 0.07 0.08 0.10 0.12

 

Voice coil material properties and selection

Voice coil skeleton materials are commonly found in Kraft Paper, Aluminium Duralumin, NOMEX, TIL, KAPTON and so on. The main features are as follows:

 

Kraft Paper PSV/PL

Cable paper (kraft paper) with a maximum continuous operating temperature of 180 oC is used, which is characterized by light weight, good insulation and low price. Its thickness is: 0.03 0.05 0.07 0.10 0.13 0.17

 

KAPTON（KSV）

Polyimide foil film, maximum continuous working temperature of 220 oC, with insulation, light weight, high strength, high temperature resistance, not easy to burn and other characteristics. KAPTON has two kinds of brown, black, black KAPTON also has the advantages of fast heat dissipation and high surface hardness.

Common wire materials are LOCK wire, SV wire, CCAW (copper-clad aluminum wire), flat wire, etc., and their main characteristics are as follows:

 

LOCK line

The operating temperature is 140 oC, it is solvent-based, and is generally used in small low-power loudspeakers.

 

SV line

With a service temperature of 200 oC, it is a solvent-based type characterized by strong bonding properties after curing, and is one of the most commonly used wire grades in voice coil production.

CCAW (copper-clad aluminum wire) is lighter than copper wire, higher conductivity and strong tensile force than aluminum wire, and its impedance is similar to copper wire at high frequencies, and the speaker made of it has good transient characteristics and high sensitivity, and is a material commonly used in high-sensitivity speakers.

 

Flat wire

The magnetic field utilization rate is larger than the round line (the magnetic field utilization rate of the circular line is 78%~91%, and the flat line is 96%), characterized by high transducer efficiency, suitable for making high-power speakers, and the flat aluminum wire is more commonly used in professional speakers (high power, high sensitivity).

Test items: inner diameter, full height, lead spacing, outlet height, reinforced paper height, tin length, roll width, impedance tolerance± 8%, polarity marking

Appearance inspection: uneven winding, loose winding, overlapping, jumper, voice coil deformation, adhesion of foreign matter, peeling test, jumper, solder joint size, unfirm, deformation.

 

2. Cotton thread

Brocade thread has the following requirements:

It has good electrical conductivity.

It has excellent folding resistance and tensile strength.

It has stable plasticity, maintains a curved image, and does not diverge into contact with other parts.

Excellent weldability.

Test items: number of strands, length± 1mm,

Appearance inspection: material, surface oxidation, loose line, stiff.

 

3. Bounce wave (positioning branch)

The main functions of the bullet wave:

The first is to fix the center position of the voice coil, so that the voice coil is kept in the middle of the magnetic gap to avoid contact between the voice coil and the magnetic circuit;

The second is to control the low-frequency resonance frequency of the speaker, limit the maximum displacement of the voice coil, avoid the voice coil from jumping out of the magnetic circuit, and provide appropriate damping for the vibration system to improve the low-frequency response and figure of merit. It is generally required that the bounce wave should have great radial rigidity and great axial compliance to ensure good mechanical strength, low resonance frequency and small distortion.

 

The common materials for elastic waves are cotton, silk, rayon, NOMEX fiber cloth, etc., which are generally hot pressed after impregnating phenolic resin alcohol solution. The commonly used shape is corrugated. The weaving method, warp and weft density, yarn count thickness, dipping concentration, forming hot pressing temperature and time of the cloth all have a great influence on the strength, compliance and fatigue resistance of the elastic wave. In addition, the size, shape, and number of ripples of the elastic wave also have an impact on its performance.

The greater the number of ripples, the deeper the ripples, and the thinner the material, the greater the compliance of the elastic waves.

Due to the limitation of the size of brackets, voice coils and other materials, the size of the bounce wave is less selectable, and its final shape and parameters must be determined according to the overall performance design requirements of the speaker in combination with the results of the material process and other tests

Test items: outer diameter, secondary outer diameter, full height, effective height, number of corrugations, hardness, whether the material and sample are the same.

Appearance: yarn, yarn, brittle hard and rotten, deformed, with debris.

 

4. Paper cone

According to the material of the edge, the paper cone can be divided into:

Full paper cone, bubble pot, rubber edge, metal basin.

 

The paper cone is divided according to the material of the cone:

Paper, used more commonly. Mainly because it can basically meet the requirements of speakers, the sound quality is soft and durable, the process is mature, and the cost is low.

Metal materials, aluminum, titanium, beryllium and their alloys, take the advantages of high modulus of elasticity.

Polymer materials, such as polypropylene, carbon fiber, bulletproof cloth, advantages: elastic mold with internal damping, good toughness, easy to shape.

 

The role of the folding ring:

Ensure that the vibrating plate has a considerable degree of freedom in the axial direction

Prevents vibration as lateral vibration

Adjust the compliance of the vibration system, thereby changing the Fo and sound quality of the speaker.

The frequency response characteristics of the speaker are largely determined by the performance of the paper cone, which in turn depends on the material, geometry and processing technology of the paper cone.

 

There are generally three requirements for paper cones:

The material density should be small,

The mechanical strength of the material should be large,

With proper internal damping.

 

In order to meet the above requirements at the same time, various measures have been taken:

Carbon fiber that penetrates the grain in the pulp. Carbon fiber is a kind of composite material, with small density, large rigidity, appropriate damping characteristics, and both heat resistance, candle resistance, stability and other advantages, used to make the speaker cone has better performance, specific performance:

The paper cone has large rigidity, and can extend the frequency range of the speaker as the piston vibration, and increase the frequency of high-frequency replay.

With the same thickness of the cone, the carbon fiber cone is light and rigid, so the output sound pressure is higher.

Due to the appropriate internal loss (damping), the split vibration of the diaphragm can be uplifted, so that the frequency response characteristics are relatively flat.

A layer of cymbals (BE) is evaporated over the paper bowl to increase the value of E/p of the paper basin.

Using metal materials (such as aluminum alloys), in order to obtain proper damping, it is often made into a multi-layer structure, and the layers are filled with high-damping resin.

The use of reinforced foamed metals, such as foam blind layers, because the porosity can be 98% larger, so the density is very small.

It adopts honeycomb plate structure. The so-called honeycomb plate structure is to use foil-like materials to assemble countless hexagonal cylinders into a honeycomb-like structure (called core), and then glue two thin plates (called skin) on both sides of the core to form a honeycomb board. The material of the core can be, aluminum, plastic, paper, etc., and the material of the skin can be carbon fiber, glass fiber, reinforced plastic, aluminum, etc.

 

The porosity of the honeycomb core is about 90%, and it is an ideal diaphragm material because the skin is made of a highly rigid material, so it has both light and rigid internal damping. At present, the membrane of flat panel speakers mostly uses this material.

Polymer composite materials are used. Such as mica and polyaryl matrix (PA) resin composed of composite materials, graphite polymer composite materials, etc., are all newly developed diaphragm materials in the world. These materials are characterized by large E/P and proper damping. Speakers made of these materials have a wide, flat frequency response and low harmonic distortion.

Structural dimension detection: outer diameter, secondary outer diameter, full height, effective height, carcass outer diameter, total weight MC ±10%, carcass MC ±10%,

Appearance inspection: defect, deformation, carcass shape.

The paper cone (carcass) is soft and hard, or the neck is not strengthened, and the color does not match the template.

Incomplete oil injection, paper cone breaks, scratches, spots, hair, poor adhesion with welt, glue, etc.

The material is bad, and the composite edge is mismatched.

 

5. Dust cover

The role is mainly dustproof, but also to improve the high-frequency effect, dust cap used to use more paper, now there are: non-woven fabric, cloth, silk, there is also metal aluminum, titanium, according to the need to choose.

Test items: outer diameter, sub-outer diameter, height, MC ±10%, appearance: deformation, scratches, folds, spots, surface dirt, material color is different from the sample.

 

Introduction to the support system

 

1. Basin rack

Commonly used is iron basin, as well as cast aluminum basin, the basin frame is mainly to play a supporting role, if the basin frame is too thin, it will also produce vibration, deformation, appearance treatment: multicolor electroplating, baking black, chrome plating, silver white and so on.

1”=25.4mm

Testing items: outer diameter, outer diameter of paper cone, mounting hole and opposite diameter, elastic wave diameter, elastic wave outer diameter, full height, effective height, thickness, terminal hole.

Appearance: deformation, breakage, deformation, scratching, scratching, poor plating, loose riveting of wass.

 

Speaker main parameters

 

Speaker main parameters

 

Speaker main parameters

 

Speaker performance is the result of the joint action of physical parameters such as electricity, mechanics, acoustics, magnetism, etc., and is determined by the performance of key components such as drum paper, bounce wave, voice coil, magnetic circuit, etc., and some of these parameters restrict and influence each other, so they must be comprehensively considered and designed.

 

The common electromechanical parameters of the speaker are briefly described as follows:

 

1. DC resistance Re

It is determined by the voice coil and can be measured directly with a DC bridge.

 

2. Resonance frequency Fo

Determined by the equivalent vibration mass Mms and equivalent ciss Cms of the loudspeaker, Fo can be measured directly with the Fo tester or obtained by measuring the impedance curve.

 

3. Maximum impedance Zo at resonant frequency

It is determined by the voice coil, magnetic circuit, and vibration system (drum paper, bounce wave), and can be measured by alternative methods or obtained by measuring impedance curves.

 

4. Equivalent radiation area Sd

只与口径(等效半径a)有关。

 

5.机电耦合因子BL

It is determined by the Bg value of the magnetic circuit and the effective length L of the voice coil line, and can also be calculated later by measuring the electrical quality factor Qes.

 

6. Equivalent vibration mass Mms

It is determined by the voice coil mass Mm1, the equivalent mass of drum paper Mm2 and the radiation quality Mmr, and Mms can be measured by the additional mass method.

 

7. Equivalent cms of cisiness

Determined by the drum paper cisis Cm1 and the bounce wave cisis Cm2, this cisis is what we call displacement, but the unit needs to be converted to the International System of Units: m/N, and the displacement can be directly measured with a positionometer. CMS can be measured by the additional volumetric method.

 

8. Equivalent volume Vas

It is only related to equivalent compliance and equivalent radiation area.

 

9. Mechanical quality factor Qms

It is determined by the equivalent vibration mass Mms, equivalent cas Cms and mechanical resistance Rms of the vibration system, and Qms can be obtained by the measurement of the impedance curve.

 

10. Electrical quality factor Qes

It is determined by the equivalent vibration mass Mms, equivalent cms of the vibration system, and electromechanical coupling factor BL, and obtained by the measurement of the impedance curve.

 

11. Total merit factor Qts

It is determined by the mechanical figure of merit Qms and the electrical figure of merit Qes.

 

12 Reference electroacoustic conversion efficiency ηo

It is determined by the electromechanical coupling factor BL, the equivalent radiation area Sd, and the equivalent vibration mass Mms.

 

13. Reference sensitivity grade SPLo

Directly related to the reference electroacoustic conversion efficiency ηo.

 

14. Reference amplitude o

It is related to the reference electroacoustic conversion efficiency ηo, electrical power Pe, equivalent radius a, frequency f

 

All of these parameters can now be measured and calculated using the speaker computer test system.